The human spine frequently requires surgery to repair deformities or injuries. Spinal problems may be caused by a trauma to the spine received during an accident, excessive strain or stress on the spine from physical activities, a sedentary lifestyle and poor posture that may place abnormal pressure on the spine, disease or a variety of other reasons. Spinal fusion is a common surgery intended to alleviate pain caused by these spinal deformities or injuries.
The spinal fusion procedure generally includes removing the disk, packing bone graft between the vertebrae and placing a spinal implant, such as screws attached to a plate, rod or cage, to fuse elements of the spine together. Once the disk is removed and the bone graft is placed between the vertebrae, the bone graft will fuse to the vertebrae over a period of several months following the surgery.
The purpose of the plate is to stabilize the vertebrae until the bone graft has become fused to the vertebrae. The plate is positioned to extend between at least two vertebrae. The plate is attached to screws anchored in each of the adjacent vertebrae, thus immobilizing the desired portion of the spine. The plate is anchored to the screws either on the front, anterior, or back, posterior, sides of the vertebrae.
The present invention is not intended to be limited to applications in a specific region of the spine, and may, in fact, be utilized equally well with the cervical, thoracic, lumbar and sacrum vertebrae of the spine. However, for purposes of explanation, the surgical procedure will be discussed in greater detail with respect only to the lumbar vertebrae region of the spine. Procedurally, anterior, or entry from the stomach region of the patient, lumbar vertebra surgery provides the surgeon with optimum access to the entire intervertebral disk. Posterior, or entry from the back of the patient, surgery is less preferred since access to the disk is restricted. Once the anterior lumbar discectomy, or removal of the lumbar disk, is completed, the bone graft is placed into the space between the vertebrae previously occupied by the disk.
The patient is then positioned for posterior fusion, or placement, of the plate. The stabilization is typically accomplished by placing a screw in each of the lumbar vertebra such the screw extends through a portion of the vertebra and into the body of the vertebra. Each screw extends posteriorly from the vertebra sufficient for attachment to the plate. The plate is then anchored to each of the screws to retain the adjacent lumbar vertebrae positioned a distance from each other. The plate and screws thereby stabilize the lumbar vertebrae and provide time for the vertebrae and bone graft to fuse into a solitary unit.
However, posterior fusion requires large posterior muscle dissection to safely implant the pedicle screws and provide for placement of the plate. Such major muscle damage presents a danger to the patient during surgery from infection and the extensive muscle damage. Also, additional time is required to perform both extensive anterior and posterior surgical portions. The added surgical time presents another risk to the patient.
Attempts to eliminate the negative aspects of posterior fusion include anterior placement of the plate and screws. Although anterior fusion avoids the problems associated with the larger posterior fusion, additional problems arise. In such systems, the anchoring screws are laterally placed on the anterior of the vertebra. Lateral placement requires a significantly more invasive procedure and much greater exposure. Also, screws anchored laterally through the anterior of the vertebra do not provide the stability of those extending posteriorly through the pedicle and into the vertebral body. Furthermore, anteriorly-anchored screws do not promote quick and uniform fusion of the bone graft to the vertebra since they do not have the stability of the pedicle fixation.
Thus a need exists for a vertebral stabilization assembly that obtains the benefits while overcoming the disadvantages of prior procedures and systems.